Hi Jkarinen,
May I ask what your system statistics are? That would be a much better guideline to go upon than what you can play on what settings. Also, may I note out, that buying eras is pointless if you possess any one of R:TW/BI, S:TW/MI or M:TW/VI - it is much easier and, probably, cheaper, to purchase each game individually rather than re-buying several games more than once. Hope this helps you, cheers!